The present invention relates to steam turbines and, more particularly, to thermal performance monitors for evaluating the instantaneous performance of steam turbine-generator systems.
Large steam turbine-generator systems represent major capital investments for their owners and their economic benefit to the owners varies with the thermal efficiency with which the steam turbines are operated. To highlight the importance of thermal efficient operation, it is believed that a difference of one percent in the efficiency of a steam turbine driving a one gigawatt electric generator is worth on the order of tens of millions of dollars over the life of the unit. Thus, the owners of a large steam turbine-generator are vitally interested in maintaining the operating parameters of the system as close as possible to the optimum set of operating parameters as designed for the system, and/or developed during operational testing following initial installation of the system, since departure from these parameters tends to reduce the thermal efficiency. In addition, unavoidable degradation in performance over time can occur due to deterioration of internal parts and other causes. Means for detecting the onset and severity of such deterioration is useful. Furthermore, it is desirable to monitor the turbine for internal problems, especially the type which necessitate rapid detection thereby permitting timely action to be taken.
Despite the importance of maintaining the operating parameters at levels which maximize thermal efficiency, in normal practice, encompassing the minute-to-minute control of the controllable parameters of a large steam turbine, the turbine shift operators customarily maintain such operating parameters at values close to optimum levels but still far enough different from the optimum to produce substantial efficiency deviations which result in cost penalties. Additionally, conventional power station instrumentation does not provide a class of information which has either the accuracy or the information content to guide an operator in adjusting and keeping a steam turbine at its best performance levels. In fact, it is possible, during the attempt to optimize system performance using monitoring systems of the prior art, for the shift operator to make adjustments which, instead of changing the operating parameters in the direction of improved efficiency, change the operating parameters in directions resulting in degraded efficiency.
As part of the installation procedure of a steam turbine-generator subsystem, it is customary for the owners and/or the contractor or turbine manufacturer to conduct very accurate tests to demonstrate or determine the heat rate of the system. Heat rate is a measure of thermal efficiency of a steam turbine-generator system defined as the number of units of thermal input per unit of electrical power output. In one convenient system of units, heat rate is measured in BTUs per kilowatt hour of power output. One standard test of heat rate is known as the ASME test and is defined in an ASME publication ANSI/ASME PTC 6 - 1976 Steam Turbines. A simplified ASME test is described in A Simplified ASME Acceptance Test Procedure for Steam Turbines,presented at the Joint Power Conference, Sept. 30, 1980, in Phoenix, Ariz. A requirement and characteristic of both of the above tests is accurate instrumentation for temperatures, pressures and flows within a steam turbine along with the resulting generator power output to determine accurately the energy content of such conditions and the resulting power output. The accuracy of measurement is sufficiently great that no measurement tolerance need be applied to the results. Such tests are costly to perform. For example, the standard ASME test requires a substantial installation of specialized measuring equipment at a substantial cost in conjunction with a great amount of manpower to administer the test. Thus, economic reality keeps the administration of such tests limited to the initial commissioning of a new steam turbine-generator system and (less frequently) to the recommissioning of a steam turbine-generator system at a subsequent time after a refurbishment.
Besides their cost, ASME-type tests have the additional drawback that they are not suitable for use in day-to-day operation of a steam turbine-generator system. The types of instrumentation required may not retain useful accuracy over extended periods. In addition, even if such testing could be conducted on a substantially concurrent, instantaneous and daily basis, the type of information conventionally produced during such tests, although invaluable in the initial engineering evaluation of the system, is of a type which requires such substantial interpretation and calculation to derive control adjustments that it is, at best, of marginal value in guiding an operator in manipulating the controls which are available to him.
Customarily, the shift operator, directly controlling the steam turbine system, does not have the time, the inclination, nor the sophistication to reduce the technical results of the ASME-type tests into an understandable format on a substantially instantaneous basis. His primary function is to monitor the turbine-generator performance as it relates to other turbine-generator sets tied into the electrical transmission system. In this view, a thermal performance monitor must gather relatively instantaneous data from the turbine-generator system and present a limited amount of information to the shift operator in a very concise, quickly readable and understandable format, such that the operator can adjust the turbine-generator set to operate more efficiently.
In contrast, a results engineer reviews the periodic performance statistics for the turbine-generator set in a more sophisticated and detailed manner. Since the results engineer's attention is not immediately focused on the steam pressures and temperatures and other parameters affecting the turbine, he can leisurely proceed with a more detailed analysis of the turbine's operation. From the results engineer's perspective, a detailed presentation at a much higher technical level of the thermal performance of each major component in the steam turbine-generator system is desirable. As an example, the detailed thermal performance data compiled, throughout one week of turbine operation, may illuminate an incipient problem with the steam condensor as reflected in an increased exhaust pressure value. By focusing his attention on the exhaust pressure vis-a-vis the other components of the turbine over an extended period of time, e.g., 2 months, the results engineer could approach the owners of the turbine-generator unit with a request for a cleaning or modification of the condensor. Further trend analysis would be facilitated by a sophisticated thermal performance monitor.
ASME-type testing can, however, be relied on initially to produce reference or a design data base from which optimum sets of operating parameters and the related heat rates and other parameters throughout a new steam turbine-generator system can be derived. Once such optimum sets of operating data are established, operating parameters during later operation of the system may be compared to it for determining correct operation of the system.